It is often desirable to drill holes of a precise length and width or to use countersinking drill bits to widen an inlet of a hole. In addition, to fasten two pieces of material together, it is necessary to drill a hole in each material. The two holes must be properly aligned and may have different widths. For example, to attach two pieces of wood used in making furniture or cabinets, a narrow hole in one piece of wood is a traction hole which receives and holds a screw. In the other piece of wood, a wider hole is drilled which is a gliding hole for slidably receiving the screw therethrough. Similar precisely sized, aligned and centered holes are needed to be drilled in many material, such as cements and plastics. Precision drilling is also very common during surgery or during treatment of bone fractures in the medical field.
For example, the treatment of bone fractures in the cranio-maxillofacial region generally proceeds by reducing the fractured bones to their anatomically correct positions, and thereafter fixing the bones in place. The bones may be fixed in place either by interosseous wiring, or by the technique of miniplate osteosynthesis. In either case, holes must be drilled in the bone structure for receiving the interosseous wire or screws for holding the miniplates to the bone.
In the drilling of holes into the bone structure, great care must be taken to ensure that the holes are drilled at precisely the correct position and to precisely the correct depth. If the holes are not drilled at the correct location, strain may be transmitted by screws to the surrounding bone structure. This may cause the bone to resorb in the vicinity of the screws resulting in loosening of the hardware.
Similarly, complications, such as blindness, extraocular muscle dysfunction, retinal or corneal damage, and severe tissue trauma could result if the depth of holes is not gauged accurately when drilling orbital bones. Accordingly, it is desirable during the drilling procedure to use an instrument which will prevent the operator from drilling too deeply into bones of cranio-maxillofacial regions. Furthermore, it is also desirable to center and align the drill bit to better control the angle of the drilling. This permits greater flexibility in the placement of implants. For example, if screws are to be placed into the frontal bone, superior to the zygomaticofrontal suture, they are preferably inserted at a downward slanting angle with respect to the forehead. This ensures that neither the screws nor the drill bit enters the anterior cranial fossa. See M. Zide, "The Placement of Screws Above the Zygomaticofrontal Suture," 48 J. Oral & Maxillofacial Surg. 813-816 (1990).
Drilling into the mandibular bone is also required for many surgical procedures such as procedures requiring implantation of various devices. One example that requires such drilling is shown in a brochure for The Bosker Transmandibular Implant (TMI) Reconstruction System, by the Walter Lorenz Surgical Instruments, Inc. of Jacksonville, Fla. The Bosker TMI uses a template with a preset drill guide. Therefore, adjustable drill guides cannot be used.
A prior art drill guide for controlling the angle and the depth of a hole drilled into anatomical bone, is disclosed in a catalog published in 1992 by Synthes Maxillofacial, a surgical supply company located in Paoli, Pa. This drill guide 1 is depicted in FIG. 1. The drill guide 1 has a threaded inner sleeve 2 which is screwed into a first opening 4a of an outer sleeve 4. By rotating the inner sleeve 2 with respect to the outer sleeve 4, the inner sleeve 2 may be extended from, or retracted into, the outer sleeve 4. A knurled nut 3 is provided which may be loosened to permit the rotation of the inner sleeve 2. After the inner sleeve 2 is adjusted to a desired length from the outer sleeve 4, the knurled nut 3 may be tightened to prevent rotation of the inner sleeve 2.
The outer sleeve 4 is attached to, and integral with, a handle 5. The outer sleeve 4 and handle 5 are connected so as to form an obtuse angle.
Such a drill guide 1 is useful in a variety of surgical operations. For example, the use of the drill guide in an exemplary surgical operation is illustrated in FIGS. 2-3 and proceeds as follows. An incision is made in the region of the fracture, the skin is retracted, and the bones are reduced to their correct anatomical positions. One or more threaded guide wires W are then inserted into the bones B having a fracture F, as depicted in FIG. 2, using a small diameter drill guide 1. The depth to which the guide wire W is inserted into the bones B is then measured by sliding a depth gauge sleeve 8 (FIG. 1) over the exposed portion of the guide wire W.
Knowing the depth of penetration of the guide wire W, the drill guide 1 may be adjusted so as to limit the drilling of a hole to a desired depth. A cannulated drill bit 6 (i.e., a drill bit with a central bore) is inserted into a distal end 4b of the outer sleeve 4 until the quick coupling 7 of the drill abuts against the distal end 4b of the outer sleeve 4 as depicted in FIG. 1. While the drill guide 1 is held in this position with one hand, the depth gauge sleeve 8 is inserted over the exposed portion of the drill bit 6a. Using the other hand, the knurled nut 3 is loosened, and the inner sleeve 2 rotated until the length of the exposed portion of the drill bit 6a equals the desired drilling depth. The knurled nut 3 is then tightened so that the inner sleeve 2 does not retract into, or extend from, the outer sleeve 4 during the drilling of the hole.
The adjusted drill guide 1 may then be inserted over the guide wire W until the inner sleeve 2 contacts the bone B, as depicted in FIG. 3. The cannulated drill bit 6 is inserted into the distal end 4b of the outer sleeve 4 of the drill guide 1 over the guide wire W. The drill is then operated to drill into the bones B until the quick coupling 7 of the drill abuts against the distal end 4b of the outer sleeve 4. Thus, the drill guide 1 acts as a stop, preventing the drilling of holes deeper than the length of the exposed portion of the drill bit 6a which protrudes from the drill guide 1 when the quick coupling 7 abuts against the distal end 4b of the outer sleeve 4.
This process is repeated using different size drill bits until a hole of desired width and depth is drilled. After the hole is drilled to the correct depth, a surgical screw is inserted into the hole and the guide wire is removed. The screws can also secure an implant, such as a miniplate, to the bone structure. The miniplate holds the bone structure together so that it can heal.
The prior art drill guides, while useful, are not entirely satisfactory for their above-described procedures. The prior art drill guides do not provide a single drill guide for aligning and centering drill bits of different thickness. Rather, according to the prior art, a different drill guide with a different width bore must be provided for each different width drill bit used in the operation. This is both inefficient and time consuming because many different size drill guides must be readily available in a sterilized condition.
Accordingly, it is an object of the present invention to overcome the disadvantages of the prior art.